On Thu, May 25, 2023 at 11:01:34PM -0700, Yonghong Song wrote:
>
>
> On 5/25/23 7:27 AM, Louis DeLosSantos wrote:
> > Add ability to specify routing table ID to the `bpf_fib_lookup` BPF
> > helper.
> >
> > A new field `tbid` is added to `struct bpf_fib_lookup` used as
> > parameters to the `bpf_fib_lookup` BPF helper.
> >
> > When the helper is called with the `BPF_FIB_LOOKUP_DIRECT` flag and the
> > `tbid` field in `struct bpf_fib_lookup` is greater then 0, the `tbid`
> > field will be used as the table ID for the fib lookup.
>
> I think table id 0 is legal in the kernel, right?
> It is probably okay to consider table id 0 not supported to
> simplify the user interface. But it would be great to
> add some explanations in the commit message.
>
> >
> > If the `tbid` does not exist the fib lookup will fail with
> > `BPF_FIB_LKUP_RET_NOT_FWDED`.
> >
> > The `tbid` field becomes a union over the vlan related output fields in
> > `struct bpf_fib_lookup` and will be zeroed immediately after usage.
> >
> > This functionality is useful in containerized environments.
> >
> > For instance, if a CNI wants to dictate the next-hop for traffic leaving
> > a container it can create a container-specific routing table and perform
> > a fib lookup against this table in a "host-net-namespace-side" TC program.
> >
> > This functionality also allows `ip rule` like functionality at the TC
> > layer, allowing an eBPF program to pick a routing table based on some
> > aspect of the sk_buff.
> >
> > As a concrete use case, this feature will be used in Cilium's SRv6 L3VPN
> > datapath.
> >
> > When egress traffic leaves a Pod an eBPF program attached by Cilium will
> > determine which VRF the egress traffic should target, and then perform a
> > FIB lookup in a specific table representing this VRF's FIB.
> >
> > Signed-off-by: Louis DeLosSantos <louis.delos.devel@xxxxxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 17 ++++++++++++++---
> > net/core/filter.c | 12 ++++++++++++
> > tools/include/uapi/linux/bpf.h | 17 ++++++++++++++---
> > 3 files changed, 40 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 1bb11a6ee6676..2096fbb328a9b 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3167,6 +3167,8 @@ union bpf_attr {
> > * **BPF_FIB_LOOKUP_DIRECT**
> > * Do a direct table lookup vs full lookup using FIB
> > * rules.
> > + * If *params*->tbid is non-zero, this value designates
> > + * a routing table ID to perform the lookup against.
> > * **BPF_FIB_LOOKUP_OUTPUT**
> > * Perform lookup from an egress perspective (default is
> > * ingress).
> > @@ -6881,9 +6883,18 @@ struct bpf_fib_lookup {
> > __u32 ipv6_dst[4]; /* in6_addr; network order */
> > };
> > - /* output */
> > - __be16 h_vlan_proto;
> > - __be16 h_vlan_TCI;
> > + union {
> > + struct {
> > + /* output */
> > + __be16 h_vlan_proto;
> > + __be16 h_vlan_TCI;
> > + };
> > + /* input: when accompanied with the 'BPF_FIB_LOOKUP_DIRECT` flag, a
> > + * specific routing table to use for the fib lookup.
> > + */
> > + __u32 tbid;
> > + };
> > +
> > __u8 smac[6]; /* ETH_ALEN */
> > __u8 dmac[6]; /* ETH_ALEN */
> > };
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 451b0ec7f2421..6f710aa0a54b3 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -5803,6 +5803,12 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
> > u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
> > struct fib_table *tb;
> > + if (params->tbid) {
> > + tbid = params->tbid;
> > + /* zero out for vlan output */
> > + params->tbid = 0;
> > + }
> > +
> > tb = fib_get_table(net, tbid);
> > if (unlikely(!tb))
> > return BPF_FIB_LKUP_RET_NOT_FWDED;
> > @@ -5936,6 +5942,12 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
> > u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
> > struct fib6_table *tb;
> > + if (params->tbid) {
> > + tbid = params->tbid;
> > + /* zero out for vlan output */
> > + params->tbid = 0;
> > + }
> > +
> > tb = ipv6_stub->fib6_get_table(net, tbid);
> > if (unlikely(!tb))
> > return BPF_FIB_LKUP_RET_NOT_FWDED;
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index 1bb11a6ee6676..2096fbb328a9b 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -3167,6 +3167,8 @@ union bpf_attr {
> > * **BPF_FIB_LOOKUP_DIRECT**
> > * Do a direct table lookup vs full lookup using FIB
> > * rules.
> > + * If *params*->tbid is non-zero, this value designates
> > + * a routing table ID to perform the lookup against.
> > * **BPF_FIB_LOOKUP_OUTPUT**
> > * Perform lookup from an egress perspective (default is
> > * ingress).
> > @@ -6881,9 +6883,18 @@ struct bpf_fib_lookup {
> > __u32 ipv6_dst[4]; /* in6_addr; network order */
> > };
> > - /* output */
> > - __be16 h_vlan_proto;
> > - __be16 h_vlan_TCI;
> > + union {
> > + struct {
> > + /* output */
> > + __be16 h_vlan_proto;
> > + __be16 h_vlan_TCI;
> > + };
> > + /* input: when accompanied with the 'BPF_FIB_LOOKUP_DIRECT` flag, a
> > + * specific routing table to use for the fib lookup.
> > + */
> > + __u32 tbid;
> > + };
> > +
> > __u8 smac[6]; /* ETH_ALEN */
> > __u8 dmac[6]; /* ETH_ALEN */
> > };
> >
> I think table id 0 is legal in the kernel, right?
> It is probably okay to consider table id 0 not supported to
> simplify the user interface. But it would be great to
> add some explanations in the commit message.
Agreed.
My initial feelings were there is no real use case to query against the Kernel's
`all` table.
The response from John will dictate if this remains the case, as the suggestion
of using a new flag bit will nullify this issue, I think.
If it stays tho, I will def add details in the commit message around this on next
rev.
